Database Management Systems:

This chapter outlines the differences between applications and database based systems. It discusses basics regarding database structure and design theory.

---

Application based approach to Event Processing: This traditional approach concentrates on the process being performed. Data play a secondary role to the programs that run in each application system. Each application collects and manages its own data, generally in dedicated, separate, physically distinguishable files for each application.

• Advantages:
  • Cheaper to implement than using the database approach
  • If the system fails, the entire organization’s information processing is not drastically interrupted
• Disadvantages:
  • Data redundancy can cause inconsistencies among the same data in different files
  • Increased storage costs because the system must store and maintain multiple versions of the same data in different files
  • Data residing in separate files are not sharable among applications
• Database Approach: Concept to decouple the data from the system application (i.e., to make the data independent of the application or other users). Facts about events are stored in relational database tables instead of separate files.
  • Just a quick side not for reference to CPA testing, they (CPA testers) recognize a databse as an integrated collection of data records and data files. It is comprised of nothing more than stored data. Database Management System (DBMS) is not a database; it is a tool. A DBMS is a seperate computer program that allows an organization to create new databases and use and work with the data in the databases after the databases have been created.
    • Advantages:
      • Solves many of the problems caused by data redundancy
      • Ease of maintenance
      • Allows multiple application programs to use the data concurrently (data independence)
      • Improves the efficiency of processing business event data
      • Reduced storage costs
      • Privacy and protects data against unauthorized disclosure, alteration, or destruction
    • Disadvantages:
      • Expensive to implement (cost of DBMS software, hardware, and employees to maintain the system)
      • If the system fails, all of the organization’s information processing halts
      • Database recovery and contingency planning are more important
      • When more than one user tries to access data at the same time, the database can face “contention” or “concurrency” problems
      • Territorial disputes over who “owns” the data
• Distinguish between logical and physical database models: The logical database view is how the data appear to the user to be stored. This view represents the structure that the user must use to extract data from the database. It is the way that a user thinks of the data in a database. The physical database storage is how the data are actually physically stored in the storage medium used in the database management system. The physical storage of the data often have little relation to the logical view.
• Data Redundancy - a disadvantage of the application approach, explain more fully the problems that can arise because of redundancy.

---

• Data Normalization: Normal forms are inclusive, in that each higher normal normal form inclues all loswer normal forms.
  • 1st Normal Form (1NF): better than table not in 1NF. Does not contain repeating groups. Designer must allocate enough columns.
    • Updates anomalies.
  • 2nd Normal Form (2NF): better than table in 1NF. A table that is in 1NF and has no partical dependencies; no non-key attribute is dependent on the primary key.
  • 3rd Normal Form (3NF): better than table in 2NF. A table that is in 2NF and has no transitive dependencies; no non-key attribute is funcitionally dependent on another non-key attribute.
• Why is data normalization such an important design characteristic of databases? Following normal forms creates tables that prevent errors/anomalies that could occur when adding/changing/deleting data stored in the database.

---